1. Field of the Invention
The present invention relates to a printer in which an ink material held in a print ribbon is transferred to a recording medium by means of a print head for recording.
2. Description of the Prior Art
A conventional printer will be first described with reference to FIGS. 6 to 10.
Referring to FIG. 6, the printer comprises a carriage 1 on which a print head is mounted, which is slidably held on a guide rod not shown and provided opposite to a platen which will be described later, a wire 2, a drive pulley around which the wire 2 is wound, a driven pulley over which the wire 2 is stretched, and a stopper 5 secured to the wire 2, the stopper 5 being arranged within a recess 1a of the carriage 1. The printer further comprises a pulley gear 6a fitted in the pulley 3, a drive source or a motor 7, and gears 8a, 8b secured to both ends of an output shaft 9 of the motor 7, one pinion gear 8a being meshed with the pulley gear 6a, the other pinion gear being meshed with a connection gear 10a. A connection gear 10b is pressed against the connection gear 10a by means of a spring 16. The pulley gear 6a is meshed with a clutch gear 11, the clutch gear 11 being disengageably connected to an electromagnetic clutch 12. A paper feed shaft 13 is connected to the electromagnetic clutch 12, so that when the clutch gear 11 is rotated under the condition that the clutch gear 11 is connected to the electromagnetic clutch 12, the shaft 13 rotates to feed a recording paper described later to a print position on the surface of the platen.
A cam gear 14 is connected to the connection gears 10a and 10b in a positional relation of meshing with each other. This cam gear 14 comprises an intermittent gear portion 14a, a gear portion 14b and a stopper portion 14c, and is in a positional relation of meshing with the connection gears 10a and 10b. Since the connection gears 10a, 10b are pressed by means of the spring 16, a force acts on the connection gear 10b so that the gear 10b may be rotated in synchronism with the connection gear 10a due to a frictional load. Therefore, when a load imposed on the connection gear 10b is greater than the frictional load, only the connection gear 10a rotates, whereas when the load on the gear 10b is smaller than the frictional load, the connection gear 10b rotates in synchronism with the connection gear 10a.
In the aforementioned printer, at a carry time, the carriage 1 moves in a direction as indicated by the arrow A in FIG. 6. At that time, as the motor 7 turns on, the connection gear 10a is rotated in a direction as indicated by the arrow b in FIG. 7 through the pinion gear 8b, and at the same time, the connection gear 10b also tends to be rotated in the direction of the arrow b. At this time, however, an actuator 18 is locked at the stopper portion 14c of the cam gear 14 meshed with the connection gear 10b, and therefore the cam gear 14 is not rotated. This increases the load toward the connection gear 10b, and the connection gear 10b is not rotated neither. During printing, a solenoid 20 is turned ON to attract the actuator 18 against the bias of the spring 19. With this, the actuator 18 is disengaged from the stopper portion 14c of the cam gear 14 with the result that the load applied to the cam gear 14 decreases. The connection gear 10b is then rotated in synchronism with the connection gear 10a and the cam gear 14 rotates in a direction as indicated by the arrow C in FIG. 7 as the connection gear 10b rotates. Upon rotation through a certain angle, the connection gear 10a is meshed with the intermittent gear portion 14a, and a drive force of the motor 7 is transmitted to the cam gear 14 directly. There is a sectoral play (not shown) between the cam gear 14 and the cam 21 fitted into the cam gear 14. During that play, the cam gear 14 is free from a load and can be rotated under the frictional load alone between the connection gears 10a and 10b. During the play, the connection gear 10a is meshed with the intermittent gear portion 14a of the cam gear 14. The cam 21 is formed with a groove cam as will be described later. A pin 17a of a lever 17 enters the groove and as a result the lever 17 swings whereby a print head is pressed against (head down) the platen.
A mechanism for movement of the print head between a print position at which it is presses against the platen and a non-print position at which it is moved away from the platen will be described in detail with reference to FIGS. 8 to 10.
As shown in FIG. 8, an L-shaped winding rack 66 is arranged parallel with a shaft 60, and both ends of the shaft 60 extend through a connection portion 67 extended from both ends of the winding rack 66 so that the winding rack 66 may be rotated around the shaft 60. A number of rack teeth 66a are provided on the front surface of the winding rack 66, the rack teeth 66a being engagable with a winding gear 61 shownin FIGS. 9 and 10 and engageable with a hook 65 fixedly mounted on the carriage 1. The lever 17 is turnably supported on the shaft 60 so that the lever 17 may be superposed on one connection portion 67 of the winding rack 66. On the end of the lever 17 extending toward the winding rack 66 is provided a projection 69 in engagement with the upper end of the connection portion 67 as shown in FIG. 8, and a tension spring 70 is stretched from the upper end of said end to the lower end of the winding rack 66. On the end of the lever 17 extending to the side opposite the winding rack 66 is provided a pin 17a, and a cam portion 21a of a cam 21 is fitted into the extreme end of the pin 17a.
In FIGS. 9 and 10, reference numeral 74 denotes a ribbon cassette encasing therein a print ribbon or the like, 75 a recording paper, 76 a pressing projection provided on the carriage 1, and 77 a carriage stopper. FIG. 9 shows a state wherein a print head 101 is arranged at a print position at which the head is pressed against a platen rubber 102 of a platen 100, namely a head-down state. FIG. 10 shows a state wherein the print head 101 is arranged at a non-print position at which the head is parted from the platen rubber 102 of the platen 100, namely, a head-up state.
When the cam 21 rotates counterclockwise from the head-up state shown in FIG. 10, the pin 17a gradually moves in a direction of moving away from the rotation center of the cam 21 along the cam groove 21a. With this movement, the lever 17 rotates clockwise around the shaft 60, and the winding rack 66 is also biased by means of the tension spring 70 for clockwise rotation therewith whereby the rack teeth 66a are disengaged from the hook 65 into engagement with the teeth of the winding gear 61 and the upper surface of the winding rack 66 comes into contact with the pressing projection 76 provided on the undersurface of the carriage 1.
With further rotation of the cam 21, the lever 17 and the winding rack 66 further rotate clockwise. With this rotation, the carriage 1 is rotated toward the platen 100, and the print head 101 mounted on the carriage 1 comes into contact with the platen rubber 102 through the recording paper 75. It is to be noted that under the condition that the winding rack 66 is rotated and the rack teeth 66a and the winding gear 61 are not meshed with each other but remain abutted, the winding rack 66 is rotated to compress a coil spring 63 and at the same time raise the winding gear 61. When the carriage 1 moves so that the teeth of the winding gear 61 arrives at a position at which the teeth mesh with the rack teeth 66a, the gear 61 is forced down by means of the coil spring 63 so that the teeth thereof are meshed with each other to rotate the winding gear 61.
With further rotation of the cam 21, the lever 17 continuously rotates clockwise whereas the winding rack 66 cannot be rotated since the print head 101 is in contact with the rubber platen 102. Thus, because the winding track 66 cannot be rotated, the lever 17 is rotated while stretching-out the tension spring 70, which force serving as a force for pressing the print head 101 after all, resulting in a load for rotating the cam 21. As shown in FIG. 9, when the pin 17a assumes a position farthest from the rotational center of the cam groove 21a, a desired pressing force F is applied to the print head 101.
FIG. 11 shows the load characteristics for pressing the print head from the head-up to head-down of the printer according to this embodiment.
As shown in FIG. 11, load is zero from the head-up state (point X) to the state (point Y) in which the print head 101 comes into contact with the platen 100 for the first time, and load a is applied to stretch the tension spring 70 from the point Y to the point Z at which a desired pressing force F is obtained following the headdown.
When the carriage 1 is drawn with the print head 101 pressed as described above, the winding gear 61 is rotated on the rack teeth 66a of the winding rack 66 as shown in FIG. 9, and the print ribbon encased in the ribbon cassette 74 is wound, according to the movement of the carriage 1, by a bobbin 64 provided integral with the winding gear 61 through the shaft 62.
In the head-down state shown in FIG. 10, the pin 17a is positioned at the end of the cam groove 21a nearest to the rotational center, and the end of the lever 17 on the side of the winding rack 66 is lowered than that of the head-down state (see FIG. 9). When the end of the lever 17 is lowered as described above, the connection portion 67 of the winding rack 66 is pressed down by the projection 69 shown in FIG. 9, and the rack teeth 66a of the winding rack 66 is downwardly oriented. The rack teeth 66a is downwardly oriented whereby the hook 65 is pressed down by the extreme end and thereby the print head 101 is held on the carriage in the state where the head is apart from the platen 100. The rack teeth 66a is downwardly oriented and therefore apart from the winding gear 61. Thus, even if the carriage 1 is reciprocated, the bobbin 64 is not rotated and winding of the print ribbon is not effected.
The print head 101 may be disengaged (head-up) in accordance with the same principle as that of the head-down. The carriage 1 is moved in the direction of arrow B in FIG. 6 when not in printing. The cam gear 14 is rotated in the direction of the arrow d in FIG. 7, and the actuator 18 and the stopper portion of the cam gear 14 always remain unlocked.
By the moving mechanism as described above, the up and down of the print head 101 is carried out at predetermined non-printing and printing positions.
In the prior art construction as described above, when the print head 101 moves up or down, the extreme ends of the gears sometimes abut each other when the connection gear 10a and the intermittent gear 14a of the cam gear 14 begin to mesh with each other, which lead to gear locking or increase in load, resulting in a disorder of the motor, a deviation in print position, and the like.